Project Summary Household contact investigation (CI) is a cornerstone of the public health response to tuberculosis (TB) in the United States. CI is also increasingly used to find missing cases and curb transmission of other infectious diseases, from sexually transmitted diseases to emerging infections such as the novel 2019 coronavirus. The practice of CI, however, raises important ethical concerns. For example, disclosure of the index patient?s disease status may be necessary to motivate participation by the household but diminishes the autonomy of the index patient and may result in stigma. In addition, performing CI during evenings, weekends, and holidays may increase convenience and yield and enable investigation of populations who may be key to disease transmission and control (e.g., mobile working young men) but may also be seen as intrusive by patients and their families. Furthermore, using CI for TB as an opportunity for HIV testing may increase efficiency but add to the stigma attached to TB. These ethical considerations are a major reason why CI has not been more widely implemented in many high-burden countries. The parent R01 for this Administrative Supplement is a randomized trial of household CI of TB in South Africa, comparing CI during routine business hours to CI during evenings and weekends in an urban province and during holiday times in a rural province. This study offers a unique opportunity to investigate these pressing ethical considerations that must be addressed if household CI is to succeed as a public health strategy in high TB/HIV burden settings. In this study, we will recruit participants in the primary R01 (after follow-up for the primary outcome) to participate in a mixed- methods investigation consisting of 300 quantitative surveys, 24 in-depth individual interviews, and six focus group discussions (10 participants each). Quantitative surveys will draw on methods from behavioral economics, including a discrete choice experiment, best-worst scaling survey, and contingent valuation study. Qualitative interviews will explore themes such as stigma, disclosure, confidentiality, and both individual and community perspectives. Both quantitative and qualitative data will be collected with an eye toward directly addressing key ethical tensions involved in the conduct of household CI. Taken together, these investigations will form the most comprehensive empiric evidence base to date on the ethics of household CI for TB in a high- burden country. This research will also directly inform policy questions relating to how household CI should be implemented and is central to the successful completion of the parent R01?s primary aims ? as these ethical issues must be addressed if any novel approach to household CI is to be successfully implemented. These considerations were also explicitly brought up during study section review; this supplement will therefore enable us to be responsive to those concerns. In summary, this research will enable us to successfully carry out our original study aims while also addressing ethical issues of critical importance to the implementation of contact investigation, a key component of the public health response to infectious disease.